In recent years, mass data is held in mobile devices, for example, in handheld smart terminals and electronic books for fast access. Such technologies have become important increasingly. Further, from the viewpoint of weight-reducing and energy-saving of information devices, integrated circuit memories having no moving parts such as a motor has proceeded rapidly. The importance in this case is how to use up memory cells in performance marginal parts on memory production. In accordance with this, lower prices and larger capacities due to improvements in productivity of memories can be realized. In addition, the reliability of data stored in such the mass-capacity memories becomes important.
Even with no large-scale technical innovation, mass-capacity memories can be realized. One such method is a multi-level technology, which can increase the storage capacity per memory cell. In addition, as the technology of insuring data for marginal memory cells, ECC is known. In particular, as for NAND flash memories, multi-levels of memory cells and ECC system technologies have been matured and almost completed.
Such the NAND flash memories have been used increasingly wider, for example, in mobile terminals and SSDs. Accordingly, it is required to achieve additional technical leaps for the NAND flash memories. For that purpose, it is required to add innovative modifications to the conventional multi-leveling technologies and ECC.
The multi-leveled NAND flash memories have been developed originally based on the specifications without consideration of multi-level. In addition, the ECC is applied to the NAND flash memories based on the technologies for the system of the overall memory. Therefore, the multi-leveling technologies and ECC have not been made optimal as the technology kept with multi-levels of memory cells.